Extreme pressure lubricant compositions



United States Patent CfiFice 3,314,888 Patented Apr. 18, 1967 This invention relates to new and useful sulfur additives for compounding extreme pressure lubricants. In particular, the invention concerns extreme pressure sulfur compounds that are relatively non-corrosive to copper and copper alloys.

The use of sulfur compounds in making extreme pressure lubricants is well-known. For example, sulfurreacted fats and fatty oils such as sulfurized sperm oil and sulfurized lard oil have been used for many years in lubricants intended for use under extreme pressure conditions such as exist in heavily loaded gears. Other examples of materials which have been sulfurized to yield useful additives include unsaturated esters such as methyl oleate, olefins and olefin polymers such as dodecene and tetraisobutylene, and alicyclics such as alpha-pinene and its homologs.

Although these compounds are generally satisfactory insofar as their primary function is concerned, which is to provide for lubrication under extreme pressure conditions, all of them are more or less deficient with respect to corrosive action on copper. In other words, whereas sulfur compounds of the types indicated above may function to improve lubrication of gears, for example, under conditions that would other-wise result in excessive wear or failure through seizure and welding, they may at the same time tend to corrode copper or bronze parts such as thrust washers, bearings, bushings, etc.

One reason for the corrosion may be found in a theory of extreme pressure additive action, which holds that it is necessary for an -EP material such as sulfur to react chemically with steel gear surfaces in order to form a chemical film, in this case iron sulfide, which actually serves as the lubricant when conditions of temperature, presure, etc. combine to destroy the mineral oil film normally present. This mode of action can be looked on as a corrosive process, in which a small amount of chemical wear is sacrificed to avoid a gross destructive failure. Unfortunately, the same chemical activity that is desirable for extreme pressure lubrication may be undesirable from the standpoint of corrosive attack on other parts which do not require an extreme pressure lubricant. It has been a problem therefore in compounding extreme presure gear lubricants to provide additives which have the necessary chemical activity insofar as the gear surfaces are concerned, but that are not so active as to cause undue corrosion of any part of the gear assembly.

It is an object of this invention to provide high pressure lubricant additives which do not cause significant copper corrosion. It has now been found that when a small effective amount of an extreme pressure additive which contains sulfur and carboxyl composition is relatively non-corrosive to copper and its alloys. The sulfur and carboxyl group-containing additives of this invention are present in the oil in a minor amount sufficient to increase the load carrying capacity of the oil, e.g. about 0.1 to 5, preferably about 0.5 to 3,

percent by weight.

The compounds of this invention are o1l-soluble to the extent necessary to impart extreme pressure properties to the base oil and may be represented by the following structural formulas:

R is an aliphatic hydrocarbon radical. of about 8 to 24 carbon atoms,

R is an aliphatic hydrocarbon radical of about 1 to 8 carbon atoms,

R" is a divalent aliphatic hydrocarbon radical of about 1 to 9 crbon atoms,

R' is an aliphatic hydrocarbon radical of about 1 to 20 carbon atoms,

11 is an integer from 0 to 1,

m equals 2n 2 equals 4n The groups R, R, R" and R' are aliphatic including cycloaliphatic hydrocarbon groups and may contain acetylenic or olefinic bonds. Preferably, however, R, R, R and R' are essentially free of ethylenic and acetylenic unsaturation, that is, all of the carbon-to-carbon linkages in the chain are not less than 1.40 A., the interatomic distance of carbon atoms in a benzene ring. The R, R, 'F" and R' can be straight or branched and may be unsubstituted or substituted with non-interfering groups such as halides, hydroxyl, etc. Examples of suitable groups are methyl, ethyl, butyl, hexyl, 2-ethyl-hexyl, octyl, dodecyl, tetradecyl, octadecyl, oleyl, cyclohexyl, other alkyl groups or the corresponding divalent alkylene groups.

The compounds of this invention may be more readily understood by reference to the following examples of their preparation.

Example I 46 grams of thioglycolic acid (0.5 mol) and 127 grams of technical mixed alpha-olefins (Archer-Daniels- Midland Co., Adacene A5'1, mixed 12 to 20 carbon atom alpha-olefins, avg. MW of 230) (0.55 mol) were mixed with 300 grams of methyl ethyl ketone solvent and 0.2 gram of benzoyl peroxide. This mixture was refluxed at 87 C. for two hours, then filtered after cooling to remove separated crystals. The product was recrystallized from acetone to yield grams of material analyzing 8.7% sulfur and having an acid number (ASTM'D 664) of 169. This product, which is presumed to be a mixed alkyl B-mercapto acetic acid, was esterified by reacting 64 grams (est. 0.2 mol) with 65 grams (0.5 mol) of 2- ethyl hexanol in 200 grams of toluene solvent and in the presence of 0.2 gram p-toluene sulfonic acid, by refluxing at 118 C. pot temperature for 5 hours. A total of 3.75 ml. of water vs. 3.6 theory (for 0.2 mol) was recovered. The final product was recovered after vacuum stripping in a yield of 86 grams of an amber liquid, analyzing 7.0% sulfur and with an acid number of 0.7.

The product of Example I has the structural formula i RSOH2O OR where R is a mixed alkyl radical of 12 to 20 carbon atoms and R is a 2-ethy1 hexyl radical.

Example II 89 grams of thiodipropionic acid (0.5 mol) and 260 grams of 2-ethyl hexanol (2 mols) were mixed with 300 grams of toluene solvent and refluxed at C. pot temmature for 23 hours with a recovery of 18.5 ml. of water s. 18.0 ml. theory. After vacuun stripping to remove olvent and excess alcohol, a yield of 188 grams of final |roduct analyzing 7.09% sulfur was obtained. The prodlct had an acid number (ASTMD 664) of 16, indicating he presence of about 2.5% unreacted acid.

The product of Example 11 has the structural formula s (CI-IzCHaPl-ORM vhere R is a Z-ethyl hexyl radical.

Example III (RSCHz 1-OCH2)2 Where R is mixed alkyl radical of 12 to 20 carbon atoms.

Example IV 34.2 grams of trimethylolethane tris (thioglycolate), equal to 0.1 mol, and 83 grams of Adacene A51 (0.36 mol) were mixed in 250 grams of toluene and 0.2 grams of benzoyl peroxide were added. The reaction mixture Was refluxed at 110 C. for six hours, followed by vacuum stripping to remove the solvent and any unreacted olefin, to yield 99 grams of product analyzing 10.0% sulfur.

The product of Example IV has the structural formula 01130 (CH2O(L/CI'I2SR)3 where R is a mixed alkyl radical of 12 to carbon atoms. Example V 43.2 grams of pentaerythritol tetrakis (thioglycolate), equal to 0.1 mol, and grams of mixed alpha olefins (Archer-Daniels-Midland Co. Adacene A-12, mixed 10 to 14 carbon atom alpha-olefins, avg. MW of 170) (0.47 mol) were mixed together with 200 grams of toluene and 0.2 gram of benzoyl peroxide was added. The reaction a solvent extracted or solvent refined mineral oil obtained in accordance with conventional methods of solvent refining lubricating oils. Generally, lubricating oils having viscosities from about 20 to 250 SUS at 210 F. are preferred. The base oil is present in major amounts and may be derived from parafiinic, naphthenic, asphaltic or mixed base petroleum crudes and if desired, a 'blend of solvent-treated Mid-Continent neutrals and Mid-Continent bright stocks may be employed. A particularly suitable base oil used in the preparation of the composition may be described as a lubricating mineral oil fraction having a viscosity index of about 100.

Synthetic hydrocarbon oils of the alkylene polymer type or those derived from coal and shale may also be employed. Alkylene oxide polymers and their derivatives such as the propylene oxide polymers and their ethers and esters in which the terminal hydroxyl groups have been modified are also suitable. Synthetic oils of the carboxylic acid ester type including di'butyl adipate, di-2-ethylhexyl sebacate, di-n-hexyl fumaric polymer, di-lauryl azelate, and the like may be used along or in blends containing complex or polyesters or other thickening agents. These esters are frequently made from dibasic acids, alcohols and glycols of 6 to 12 carbon atoms.

If desired other additives may be included in the lubricating oil composition of the present invention so long as they do not adversely affect the load carrying properties of the oil and its tendency not to corrode copper. The additives can be for example, extreme pressure agents, pour depressors, corrosion inhibitors, anti-foam agents, etc.

The additives of this invention were evaluated in lubricant compositions by the Falex and SAE machine maximum load tests. These tests are well-known in the art, and a description of the detailed operating procedures are not repeated here. However, such details are given in Volume 32 of the Journal of the Institute of Petroleum, April 1946, for the Falex test; and in the CRC reference handbook under the designation L-17-545 for the SAE test. The lubricant compositions were also tested for copper corrosion by the well-known ASTM Standards test D130 at 212 F.

Examples VI to XIV The tests referred to were made on blends of the sulfur additives in a 200 SUS at 100 neutral oil at equal sulfur content in order to clearly demonstrate the efficacy of the sulfur as contained in the compounds of this invention. Results are shown in the following table.

TABLE Wt. Percent Falex Load, SAE Load, ASTM D130 Sample Additive (Percent in Blend) Added Sulfur lbs. lbs. Copper in Blend Corrosion Dodecylmereapto methane CII2 SC12II25 2 (1.0%). 0.15 1 Suliurized dodeeene (0.6% 0.15 4 Sulfurized methyl oleate (1.0%) 0. 15 3 Compound of Example I (1.0%). 0. 15 1 Compound of Example II (2.2%)... 0.15 1 Compound of Example 111 (1.6%) 0.15 1 Compound of Example IV (1.6%) 0.15 1 Compound of Example V (1.4%)... 0.15 1, 500 410 1 None None 1, 000 90 1 mixture was refluxed at 115 C. for six hours, after which the solvent and any unreacted olefin were removed by vacuum stripping, yielding 103 grams of product analyzing 11.1% sulfur.

The product of Example V has the structural formula otol-rzoiiol-rsnni where R is a mixed alkyl radical having from 10 to 14 carbon atoms.

The lubricating oil base stock used in the present invention is of lubricating viscosity and can be, for instance,

These data demonstrate that the compounds of this invention prov1de extreme pressure lubricants which are and a small amount effective to increase the load carrying capacity of the base oil of an oil-soluble additive having the structure R'.,-o-(R"-o- 'i-R"-sR),

Where R is an aliphatic hydrocarbon radical of about 8 to 24 carbon atoms, R is an aliphatic hydrocarbon radical of about 1 to 8 carbon atoms, R" is a divalent aliphatic hydrocarbon radical of about 1 to 9 carbon atoms, n is an integer from 0 to 1, and tequals 4n.

2. A lubricating oil composition consisting essentially of a major amount of a base oil of lubricating viscosity and about 0.1 to 5 weight percent of an oil-soluble additive having the structure 0 R,,C(R-O-iiRS-R-)t Where R is an aliphatic hydrocarbon radical of about 8 to 24 carbon atoms, R is an aliphatic hydrocarbon radical of about 1 to 8 carbon atoms, R is a divalent aliphatic hydrocarbon radical of about 1 to 9 carbon atoms, n is an integer from 0 to 1, and t equals 4-n.

3. The composition of claim 1 wherein the additive is i CH C(CH OGCHzSR)s wherein R is an alkyl radical of 12 to 20 carbon atoms. 4. The composition of claim 1 wherein the additive is 0 II o (CHZOCCHQSRWIH wherein R is an alkyl radical of 10 to 14 carbon atoms.

References Cited by the Examiner UNITED STATES PATENTS 2,216,751 10/1940 Rosen 252-486 2,683,119 7/1954 Smith et al 25248.6 2,947,599 8/1960 Ennis 25248.6 3,144,422 8/1964 Homberg 260-481 3,158,576 11/1964 Rudel et a1 252-48.6 3,189,547 6/1965 Calhoun 25248.6

DANIEL E. WYMAN, Primary Examiner. L. G. XIARHOS, Assistant Examiner. 

1. A LUBRICATING OIL COMPOSITION CONSISTING ESSENTIALLY OF A MAJOR AMOUNT OF A BASE OIL OF LUBRICATING VISCOSITY AND A SMALL AMOUNT EFFECTIVE TO INCREASE THE LOAD CARRYING CAPACITY OF THE BASE OIL OF AN OIL-SOLUBLE ADDITIVE HAVING THE STRUCTURE 